I searched the forum but I found no answer. After an hour or so of searching the Internet I finally found the answer, so I thought I would post it here.
Press the button/front of the Radiator Thermostat for approximately 10 seconds and there will be a green rim of light and the Networking symbol will be blinking on the screen. When it is blinking you can easily find the thermostat in the Zigbee Home Automation integration.